XsLTPG31 Confers Leaf Cuticular Wax Deposition and Drought Resistance in Yellowhorn

With increasing frequency and severity under climate change, drought stress has become a predominant abiotic limiting factor of global plant productivity. Yellowhorn (Xanthoceras sorbifolium Bunge), an endemic species of woody oil tree in North China, has substantial developmental potential in arid and semi-arid regions. To elucidate the genetic basis of its drought response, a genome-wide association study (GWAS) of 13 leaf anatomical structure traits across 237 yellowhorn accessions was performed in this study, and 21 candidate genes that regulate leaf structural variation were identified. Among these genes, XsLTPG31, which encodes a nonspecific lipid transfer protein, was significantly induced by drought stress. Heterologous overexpression of XsLTPG31 in Arabidopsis, its transient overexpression in yellowhorn leaves, and virus-induced gene silencing (VIGS) of XsLTPG31 demonstrated that XsLTPG31 promotes the deposition of leaf epidermal wax and modulates drought resistance through facilitating the export of wax to the extracellular space. Moreover, we revealed that XsLTPG31 is directly activated by XsMYB16 via promoter binding. Taken together, the results of our study enhance the understanding of the regulatory mechanisms underlying LTPG-mediated cuticular wax deposition and might provide targets for the breeding of drought-tolerant varieties of yellowhorn.